Any good methods for this?
The ports were leaking at one time, and left streaks running down below them. Just about 1" wide.
The teak is oiled.
Not sure how to refinish. Just oiling would make it all darker, including the stains.

I almost bought a boat with damage on the interior wood panels from left open hatches. Could not find any satisfactory way to cure it other than replacing the panels. Cutting back the varnish and refinishing did not help (we experimented with a couple of spots) because the wood was blackened by the soaked-in water. We also tried painting over them and imitating the grain -- a highly skilled cabinet maker did this. Looked like complete cr*p. Sorry if that is unhelpful, but it was my experience.

If you have white streaks, on the other hand, like coffee cup rings on a table -- this can be solved with a piece of cloth and an iron, like for ironing clothes.

Solution of Oxalic acid can sometimes be used to get black/blue stains out of Oak furniture. Might work on Teak as well. Warning it takes a long time soaking, but it worked for me on Oak a couple of times.

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